The present invention relates to techniques for use in a storage subsystem and an information processing system, and in particular to techniques for detecting and recovering from errors occurring in storage subsystems having two or more components linked together by a communication link with a loop topology such as the fibre channel loop.
Conventional high capacity storage subsystems can be comprised of two or more hard disk drives which are connected by a Fibre Channel (FC). In the connecting topology of the FC Loop (FIBRE CHANNEL ARBITRATED LOOP (FC-AL)), each drive and a controller which controls the drive in the storage subsystem are connected with one another by a loop topology. A port bypass circuit (PBC) is installed in a connecting part between each drive and the FC Loop in order to disconnect the drive from the FC Loop when the drive incurs a failure or is to be replaced by another drive.
The Fibre Channel, one of the super gigabit technologies, has been standardized under the name, “ANSI NCITS T11” (ANSI X3 T11 by former name).
While certain advantages are perceived, opportunities for further improvement exist. For example, according to conventional FC Loop technology, once the fibre channel loop is broken at any point, it becomes substantially impossible to communicate between a controller and each drive connected to the fibre channel loop.
What is needed are techniques for improving for detecting and recovering from errors occurring in disk drive subsystems having a controller and drive units connected by a fibre channel loop.